Mosquitoes may learn DEET means food, lab finds

Mosquitoes can – A lab study in Journal of Experimental Biology reports that yellow fever mosquitoes (Aedes aegypti) can be trained to associate the repellent DEET with a blood meal. Researchers say the result points to DEET being detectable rather than purely masking human sc

For decades, DEET has been the go-to chemical defense against mosquitoes. The idea is simple: make your skin smell or taste unpleasant to a hunter that wants blood.

But in a new lab study, that logic gets complicated. When yellow fever mosquitoes (Aedes aegypti) were exposed to DEET, they learned to associate the chemical with food.

The study was reported May 28 in the Journal of Experimental Biology, and it centers on whether insects can turn an off-putting odor into something they’ll seek out—if they’ve been “trained” to link it to a reward.

DEET has been a “gold standard” in insect repellent for decades. Yet researchers still don’t fully agree on how it works. Clément Vinauger, a neuroethologist at Virginia Tech in Blacksburg, says the mystery remains. Some studies have suggested mosquitoes dislike the way DEET smells or tastes. Others point in a different direction: DEET may scramble mosquito senses so they can’t detect enticing body odors that would normally lure them in for a blood meal.

In the experiments, the researchers set out to test a more behavioral question—whether mosquitoes can detect DEET and whether experience can reshape their response to it.

Vinauger and colleagues housed mosquitoes in a central container connected to two flasks. One flask held clean air; the other held DEET. The mosquitoes were then allowed to feed on blood from an artificial feeder while they were exposed only to clean air for 10 seconds.

After that brief “clean air” feeding window, the team cranked up the DEET exposure, aiming to train the insects to associate the repellent with a meal.

To see whether the mosquitoes actually learned the connection, the researchers tested trained and untrained mosquitoes in narrow tubes. A team member held an untreated hand a few centimeters from one end of the tube and a hand sprayed with a DEET-containing repellent at the other end. The trained mosquitoes attempted to bite the repellent-treated hand. Untrained mosquitoes steered clear.

The results suggest two things at once. First, the mosquitoes are able to smell DEET. Second, their behavior can change depending on prior experience.

Anandasankar Ray, a neuroscientist at the University of California, Riverside, who was not involved in the work, said the study supports the idea that DEET is being detected rather than simply masking scent. “And [mosquitoes] can be trained to be attracted to it by offering a reward with it.”

Ray also raised a key detail that complicates any attempt to extrapolate directly to real life: mosquitoes don’t only use their antennae to smell. They also smell with their legs, and in these experiments the insects were not able to land on the repellent-treated hand.

Because mosquitoes land on skin to take blood, Ray argued that DEET should repel them before they can start feeding. He described what the insects likely experienced in the tube test as a mismatch: “You’d be getting the smell of DEET being paired with a bitter touch contact. ” he said. “It would be a punishment for them rather than a reward.”.

Vinauger offered a different scenario for how learning might happen outside the lab. He suspects mosquitoes could learn to associate DEET with a meal when the repellent effects have largely worn off—perhaps hours after people apply it to their skin. In that window. traces of DEET might still be present on the surface. but maybe not enough to trigger the strong repellency effect that normally prevents bites.

If mosquitoes can land, drink blood, and not be repelled, Vinauger said, they may then learn to link the chemical’s smell with the meal and begin hunting for a combination of human odor and DEET.

For most people, the practical message is still protective—at least, as far as the study’s author is concerned. The results do not suggest people should stop using DEET.

“It’s still the gold standard in terms of protection,” Vinauger said.

Even so. the study touches something many users already know but rarely think about: DEET products are sold by different manufacturers at varying concentrations. and each product comes with unique instructions. Vinauger emphasized that proper use matters. “Flipping that bottle and reading the label,” he said, “is important.”.

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